REGULATING PULSE WIDTH MODULATORS

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SG3525A

REGULATING PULSE WIDTH MODULATORS

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8 TO 35 V OPERATION

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5.1 V REFERENCE TRIMMED TO±1 %

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100 Hz TO 500 KHz OSCILLATOR RANGE

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SEPARATE OSCILLATOR SYNC TERMINAL

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ADJUSTABLE DEADTIME CONTROL

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INTERNAL SOFT-START

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PULSE-BY-PULSE SHUTDOWN

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INPUT UNDERVOLTAGE LOCKOUT WITH HYSTERESIS

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LATCHING PWM TO PREVENT MULTIPLE PULSES

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DUAL SOURCE/SINK OUTPUT DRIVERS DESCRIPTION

The SG3525Aseries of pulse width modulator inte- grated circuits are designed to offer improved per- formance and lowered external parts count when used in designing all types of switching power supplies. The on-chip + 5.1 V reference is trimmed to± 1 % and the input common-mode range of the error amplifier includes the reference voltage eliminating external resistors. A sync input to the oscillator al- lows multiple units to be slaved or a single unit to be synchronized to an external system clock. A single resistor betweenthe CTandthe dischargeterminals provide a wide range of dead time ad- justment.

Thesedevicesalso featurebuilt-insoft-startcircuitry with only an external timing capacitor required. A shutdownterminal controls both the soft-start circu- ity and the output stages, providing instantaneous

turn off through the PWM latch with pulsed shutdown, as well as soft-start recycle with longer shutdown commands. These functions are also controlled by an undervoltagelockout which keepsthe outputs off and the soft-start capacitor discharged for sub-normal input voltages. This lockout circuitry includes approximately 500 mV of hysteresis for jitter- free operation. Another feature of these PWM circuits is a latch following the comparator. Once a PWM pulses has been terminated for any reason, the outputs will remain off for the duration of the pe- riod. The latch is reset with each clock pulse. The output stages are totem-pole designs capable of sourcing or sinking in excess of 200 mA. The SG3525Aoutput stage features NOR logic, giving a LOW output for an OFF state.

DIP16 16(Narrow)

Type Plastic DIP SO16

SG2525A SG2525AN SG2525AP

SG3525A SG3525AN SG3525AP

PIN CONNECTIONS AND ORDERING NUMBERS (top view)

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ABSOLUTE MAXIMUM RATINGS

Symbol Parameter Value Unit

Vi Supply Voltage 40 V

VC Collector Supply Voltage 40 V

I_OSC Oscillator Charging Current 5 mA

Io Output Current, Source or Sink 500 mA

IR Reference Output Current 50 mA

IT Current through CTTerminal Logic Inputs

Analog Inputs

5 – 0.3 to + 5.5

– 0.3 to Vi

mA V V

P_tot Total Power Dissipation at T_amb= 70°C 1000 mW

Tj Junction Temperature Range – 55 to 150 °C

T_stg Storage Temperature Range – 65 to 150 °C

Top Operating Ambient Temperature : SG2525A SG3525A

– 25 to 85 0 to 70

°C°C

THERMAL DATA

Symbol Parameter SO16 DIP16 Unit

Rth j-pins

Rth j-amb

Rth j-alumina

Thermal Resistance Junction-pins Max

Thermal Resistance Junction-ambient Max

Thermal Resistance Junction-alumina (*) Max 50

50 80

°C/W°C/W

°C/W

* Thermalresistance junction-alumina with the device soldered on themiddle ofan alumina supporting substrate measuring 15×20 mm ; 0.65 mm thickness with infinite heatsink.

BLOCK DIAGRAM

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ELECTRICAL CHARACTERISTICS

(V# i = 20 V, and over operating temperature, unless otherwise specified)

Symbol Parameter Test Conditions SG2525A SG3525A

Unit Min. Typ. Max. Min. Typ. Max.

REFERENCE SECTION

VREF Output Voltage Tj= 25°C 5.05 5.1 5.15 5 5.1 5.2 V

∆VREF Line Regulation Vi= 8 to 35 V 10 20 10 20 mV

∆VREF Load Regulation IL= 0 to 20 mA 20 50 20 50 mV

∆V_REF/∆T* Temp. Stability Over Operating Range 20 50 20 50 mV

* Total Output Variation Line, Load and Temperature

5 5.2 4.95 5.25 V

Short Circuit Current VREF= 0 Tj= 25°C 80 100 80 100 mA

* Output Noise Voltage 10 Hz≤f≤10 kHz, Tj= 25°C

40 200 40 200 µVrms

∆VREF* Long Term Stability Tj= 125°C, 1000 hrs 20 50 20 50 mV OSCILLATOR SECTION * *

*, • Initial Accuracy Tj= 25°C ±2 ±6 ±2 ±6 %

*, • Voltage Stability Vi= 8 to 35 V ±0.3 ±1 ±1 ±2 %

∆f/∆T* Temperature Stability Over Operating Range ±3 ±6 ±3 ±6 %

f_MIN Minimum Frequency R_T= 200 KΩC_T= 0.1µF 120 120 Hz

f_MAX Maximum Frequency R_T= 2 KΩC_T= 470 pF 400 400 KHz

Current Mirror IRT= 2 mA 1.7 2 2.2 1.7 2 2.2 mA

*, • Clock Amplitude 3 3.5 3 3.5 V

*, • Clock Width Tj= 25°C 0.3 0.5 1 0.3 0.5 1 µs

Sync Threshold 1.2 2 2.8 1.2 2 2.8 V

Sync Input Current Sync Voltage = 3.5 V 1 2.5 1 2.5 mA

ERROR AMPLIFIER SECTION (V_CM= 5.1 V)

VOS Input Offset Voltage 0.5 5 2 10 mV

I_b Input Bias Current 1 10 1 10 µA

Ios Input Offset Current 1 1 µA

DC Open Loop Gain RL≥10 MΩ 60 75 60 75 dB

* Gain Bandwidth Product

Gv= 0 dB Tj= 25°C 1 2 1 2 MHz

*, ❚ DC Transconduct. 30 KΩ ≤RL≤1 MΩ

Tj= 25°C 1.1 1.5 1.1 1.5 ms

Output Low Level 0.2 0.5 0.2 0.5 V

Output High Level 3.8 5.6 3.8 5.6 V

CMR Comm. Mode Reject. VCM= 1.5 to 5.2 V 60 75 60 75 dB

PSR Supply Voltage Rejection

V_i= 8 to 35 V 50 60 50 60 dB

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ELECTRICAL CHARACTERISTICS (continued)

Symbol Parameter Test Conditions SG2525A SG3525A

Unit Min. Typ. Max. Min. Typ. Max.

PWM COMPARATOR

Minimum Duty-cycle 0 0 %

• Maximum Duty-cycle 45 49 45 49 %

• Input Threshold Zero Duty-cycle 0.7 0.9 0.7 0.9 V

Maximum Duty-cycle 3.3 3.6 3.3 3.6 V

* Input Bias Current 0.05 1 0.05 1 µA

SHUTDOWN SECTION

Soft Start Current VSD= 0 V, VSS= 0 V 25 50 80 25 50 80 µA

Soft Start Low Level VSD= 2.5 V 0.4 0.7 0.4 0.7 V

Shutdown Threshold To outputs, VSS= 5.1 V

Tj= 25°C 0.6 0.8 1 0.6 0.8 1 V

Shutdown Input Current V_SD= 2.5 V 0.4 1 0.4 1 mA

* Shutdown Delay VSD= 2.5 V Tj= 25°C 0.2 0.5 0.2 0.5 µs

OUTPUT DRIVERS (each output) (VC= 20 V)

Output Low Level Isink= 20 mA 0.2 0.4 0.2 0.4 V

Isink= 100 mA 1 2 1 2 V

Output High Level I_source= 20 mA 18 19 18 19 V

I_source= 100 mA 17 18 17 18 V

Under-Voltage Lockout V_compand V_ss= High 6 7 8 6 7 8 V

I_C Collector Leakage V_C= 35 V 200 200 µA

tr* Rise Time CL= 1 nF, Tj= 25°C 100 600 100 600 ns

tf* Fall Time CL= 1 nF, Tj= 25°C 50 300 50 300 ns

TOTAL STANDBY CURRENT

Is Supply Current Vi= 35 V 14 20 14 20 mA

* These parameters, although guaranteed over the recommended operating conditions, are not 100 % tested in production.

• Tested at fosc= 40 KHz (RT= 3.6 KΩ, CT= 10nF, RD= 0Ω). Approximate oscillator frequency is defined by : f = 1

CT(0.7 RT+ 3 RD)

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DC transconductance (gM) relates to DC open-loop voltage gain (Gv) according to the following equation : Gv= gMRLwhere RLis the resistance from pin 9 to ground. The minimum gMspecification is used to calculate minimum Gvwhen the error amplifier output is loaded.

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TEST CIRCUIT

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Figure 1 : Oscillator Charge Time vs. RT

and CT.

Figure 2 : Oscillator Discharge Time vs. RD

and CT. RECOMMENDED OPERATING CONDITIONS (•)

Parameter Value

Input Voltage (Vi) 8 to 35 V

Collector Supply Voltage (VC) 4.5 to 35 V

Sink/Source Load Current (steady state) 0 to 100 mA

Sink/Source Load Current (peak) 0 to 400 mA

Reference Load Current 0 to 20 mA

Oscillator Frequency Range 100 Hz to 400 KHz

Oscillator Timing Resistor 2 KΩto 150 KΩ

Oscillator Timing Capacitor 0.001µF to 0.1µF

Dead Time Resistor Range 0 to 500Ω

• (

⋅

⁾Range over which the device is functional and parameter limits are guaranteed.

Figure 3 : Output Saturation Characteristics.

Figure 4 : Error Amplifier Voltage Gain and Phase vs. Frequency.

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SHUTDOWN OPTIONS (see Block Diagram) Since both the compensation and soft-start termi- nals (Pins 9 and 8) have current source pull-ups, either can readily accept a pull-down signal which only has to sink a maximum of 100 µAto turn off the outputs.This is subject to the added requirement of discharging whatever external capacitance may be attached to these pins.

An alternateapproachis the useof the shutdowncir- cuitry of Pin 10 which has been improved to en- hance the available shutdown options. Activating this circuit by applying a positive signal on Pin 10 performs two functions : the PWM latch is immedi-

ately set providing the fastest turn-off signal to the outputs ; and a 150µA current sink begins to discharge the external soft-start capacitor. If the shutdown command is short, the PWM signal is terminated without significant discharge of the soft-start capacitor, thus, allowing, for example, a convenient implementation of pulse-by-pulse current limiting.

Holding Pin 10 high for a longer duration, however, will ultimately discharge this external capacitor, re- cycling slow turn-on upon release.

Pin 10 should not be left floating as noise pickup could conceivably interrupt normal operation.

Figure 5 : Error Amplifier.

PRINCIPLES OF OPERATION

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Figure 7 : Output Circuit (1/2 circuit shown).

Figure 6 : Oscillator Schematic.

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Figure 10. Figure 11.

For single-ended supplies, the driver outputs are grounded.The VCterminal is switched to groundby the totem-pole source transistors on alternate oscillator cycles.

In conventional push-pull bipolar designs, forward base drive is controlled by R1- R3. Rapid turn-off times for the power devices are achieved with speed-up capacitors C1and C2.

Figure 8. Figure 9.

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DIP16

DIM. mm inch

MIN. TYP. MAX. MIN. TYP. MAX.

a1 0.51 0.020

B 0.77 1.65 0.030 0.065

b 0.5 0.020

b1 0.25 0.010

D 20 0.787

E 8.5 0.335

e 2.54 0.100

e3 17.78 0.700

F 7.1 0.280

I 5.1 0.201

L 3.3 0.130

Z 1.27 0.050

OUTLINE AND

MECHANICAL DATA

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SO16 Narrow

DIM. mm inch

MIN. TYP. MAX. MIN. TYP. MAX.

A 1.75 0.069

a1 0.1 0.25 0.004 0.009

a2 1.6 0.063

b 0.35 0.46 0.014 0.018

b1 0.19 0.25 0.007 0.010

C 0.5 0.020

c1 45°(typ.)

D (1) 9.8 10 0.386 0.394

E 5.8 6.2 0.228 0.244

e 1.27 0.050

e3 8.89 0.350

F (1) 3.8 4 0.150 0.157

G 4.6 5.3 0.181 0.209

L 0.4 1.27 0.016 0.050

M 0.62 0.024

S

(1) D and F do not include mold flash or protrusions. Mold flash or potrusions shall not exceed 0.15mm (.006inch).

OUTLINE AND MECHANICAL DATA

8°(max.)

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